Radiation: Effects and Safety

A.K. BhatiCentre of Advanced Study in Physics

Panjab University, Chandigarh

What is Radiation?

Radiation is the process of emitting energy through a medium or space in the form of waves or particles

Radiation

Non-ionizing Ionizing

Directly ionizing (Charged particles)

electrons, protons,alpha particles etc.

Indirectly ionizing (neutral particles)

photons, neutrons etc.

Source of Radiations

Decay of Radioactive Nuclei(-, +, , -rays)

Production of Radiation Beams in Accelerators, Nuclear Reactors etc.

X-ray equipments

Natural Radiations(Cosmic, Terrestrial and internal radiations)

Strength of Source No. of disintegrations per unit time[Becquerel (Bq), Curie (Ci)]

Interaction with Matter

1. Uncharged Radiation Characterized by

Long distance without interactions

Major modifications during the stochastic interactions and therefore by exponential attenuation.

2. Charged Radiations Characterized by

Many small interactions by continuous showing down

A finite range

Two Types of Events in Materials

1. Disordering of the crystalline structure due to atomic displacements, thermal spike effects or nuclear transformation.

2. Ionization and electron transport which can cause changes in chemical or biological properties, increases conductivity, free radical formation and polarization or space change effect.

Action of Radiation at the Biological Level1. Absorbed dose (D): Energy deposited by any type of radiation per

unit mass in any target material.

Unit: Joule per kilogram (J/Kg) or 1 gray (Gy) Old unit: rad (0.01 Gy)

2. Equivalent dose (H): used to quantify the biological effect of dose to individual organs

H = D x WR WR – Radiation weighting factor – associated with the energy distribution at the

cellular level – 1 for x & -rays and electrons, and 20 for -rays

3. Effective dose (E): Takes into account the varying sensitivity of different tissues to radiation E = =

WT – Tissue weighting factor – 0.12 for bone marrow

– 0.05 for liver – 0.01 for skin

Effects of Radiation on CellsAt the cellular level the radiation interacts with the DNA of cell.

Excitations - consumes the most energy

Ionization - Leads to biological effects via the disruption of

chemical bonds.

DNA damage can occur in two different ways:1. Direct interaction – single and double stand breaks, base damages, cross-links between different strands of DNA,

protein cross-links and intercalations etc

2. Indirect interaction- Through radical formation, mostly in water , (H+ and OH-) OH- radical is highly reactive. There are many different chemical reactions involving the products of radiation interaction with water, e.g.,

OH-+OH- H2O2

These changes can induce- A correct repair of the DNA by the protection mechanisms of

the cell. An erroneous repair of the DNA leading to viable cell. One of

the important mechanism for the induction of the cancer.

Effects of the irradiation on the organism - 1. Deterministic effect- - Associated with the destruction of the great number of cells

with in the organ in question. These are characterized by.- The presence of the dose threshold- Dysfunction of the organ- A severity of the effect that is function of the dose and generally an immediate occurrence (few hours to few weeks).

2. Stochastic effect- characterized by a modification at the cellular level and

- the absence of a demonstrated threshold- a probabilities of occurrence depending on the dose and a major latency period.

Risk of cancer induction (based on survivors of the bombing of Hiroshima and Nagasaki):- Probability of cancer induction is linear without threshold.- The risk factor for fetal cancer induction is estimated to 4.0 X 10-5 mSv-1

- The minimal latency period for cancer induction is of 2 years for leukemia and 10 years for solid tumors.

Hereditary effect of the radiation:

No evidence in human population is observed. The risk factor for hereditary disorders induction is estimated to 1.0 X 10-5 mSv-1 (through the extrapolation of results on animals).

Principles and Methods of Radiation Protection

Aim of radiation protection-

to protect man and his descendants

the environment against the harmful effects of ionizing

radiation Objective of radiation protection-

to prevent every deterministic effect of the radiation

to limit the probability of stochastic effects to an

acceptable level

Objective are achieved through-

Justification

Optimization

limitation

- of the individual doses

Accessibility to areas- 1. Supervised area: Work sector where a person can

receive an annual effective dose higher than 1 mSv, but lower than 6 mSv.

2. Controlled area: Working sector where a person can receive an annual dose higher than 6 Sv

Protection methods- External exposure-

- limitation of the duration of the stay in the radiation field

- the holding of the greatest distance to the source - the use of shielding between the source and the person

Exposure due to incorporation - isolation of the radioactive substance (use of ventilation

hoods, glove boxes and recovery containers etc.)- isolation of the person (use of laboratory cloths, gloves and

masks) isolate the substance-isolate the person.

Operational dosimetric quantities: representative of the limited quantities and easy measurable.

1. Ambient equivalent dose H*(10) – for the monitoring of external radiation

2. Individual equivalent doses Hp(10) and Hp(0,07) – for the personal dosimetry based on the wearing of a personal passive dosimeter or an active dosimeter.

The monitoring of incorporation is based on the measurement of the radiation emitted by the incorporated radioactive substances or on the measurement of the urine activity (determination of the E50).

3. Occupational exposures – lead to an average individual dose of the order of 0.1 mSv (1 mSv for nuclear power plants).

Legislation (radioactive protection): Comprises –- International recommendations- National laws and internal regulations of the company

Objective of the legislation:- Protection of man and the environment- the principles of authorization for the use of ionizing radiations and of the surveillance by the authorities - Management of radioactive waste- Management of the organization in case of a radiological emergency

By an operation in supervise or controlled area the following practical rules are applicable:

- to limit the access to these area to the work necessities;

- to reduce the number persons in the controlled area;

- to prepare the operation before entering the regulated area;

- to wear the individual dosimeter and, if necessary, an operational dosimeter;

- to use the radioactive waste container for small quantities of waste as mentioned on the containers;

- to let control by the radiation protection group the contamination of material before removing it out of the

area;

- to obtain a special authorization for work in the accelerator tunnels;

- not to drink or eat in the regulated area;

- not to remove or displace warning panels.

Particular rules must applied in the following situations:

- intervention with the risk of contamination;

- use of radioactive source;

- industrial radiography in the sector;

- management of radioactive waste;

- transport of radioactive material from the

experimental site.

Thankyou